* Fractured gas produces 30 pct more emissions than oil
* Gas industry argues no hard data to support study
PHILADELPHIA, March 31 (Reuters) - Natural gas obtained by the controversial technique of hydraulic fracturing may contribute significantly to greenhouse gas emissions and so should not be considered as a cleaner alternative to coal or oil, according to a Cornell University researcher.
Although natural gas, when burned, produces only about half of the carbon dioxide emissions of coal, that calculation omits greenhouse gas emissions from the well-drilling, water-trucking, pipeline-laying, and forest-felling that are part of the production of hydraulically fractured natural gas, Ecology Professor Robert Howarth argues in a new paper.
Combining the effects of combustion, production, distribution, and leaked methane from hydraulically fractured natural gas gives the fuel about the same greenhouse gas emissions as coal and about 30 percent more than diesel or gasoline, Howarth says in the draft paper published in mid-March.
"A complete consideration of all emissions from using natural gas seems likely to make natural gas far less attractive than other fossil fuels in terms of the consequences for global warming," Howarth writes.
Energy companies are scrambling to develop vast reserves of natural gas from deep shale beds in many U.S. states including Texas, Louisiana, and Pennsylvania. Experts say shale gas could meet national demand for a century while helping to reduce carbon emissions and reducing petroleum imports.
"Government and industry should not be moving ahead on the basis of what is already misleading and incomplete information," Howarth told Reuters. He urged a moratorium on further development in the multibillion-dollar industry until more is known about its greenhouse gas emissions.
The damaging nature of gas from fracturing, or "fracking", undermines claims that it is a "transition" fuel between carbon-intensive sources like coal, and renewables such as solar and wind, Howarth said in the paper.
Citing preliminary data, Howarth estimates total greenhouse gas emissions from hydraulically fractured natural gas may be equivalent to 33 carbon grams of CO2, slightly more than 31.9 grams for coal, and well above the 20.3 grams for diesel or gasoline.
The data are partly based on methane leakage of 1.5 percent of natural gas consumed, a figure assumed by the federal government.
Claims by energy companies that natural gas is a cleaner alternative to coal and oil are further undermined by leaked methane - the principal component of natural gas -- which is many times more potent as a greenhouse gas component than CO2, argued Howarth, who has served on National Academy of Sciences panels looking into climate change, and has been a Cornell professor since 1985.
Dan Whitten, a spokesman for America's Natural Gas Alliance, an industry group, dismissed Howarth's assertions as preliminary and speculative and not backed by hard data and said the professor's statement undermined its own credibility.
"We concur with the author's own assessment that this two-page draft is 'highly uncertain', that the 'numbers should be treated with caution', and that there is 'no rigorous estimate' to support its conclusions," Whitten said.
"Natural gas is twice as clean as coal and is available here in America in significant abundance today," Whitten added.
"Alongside the development of renewables, natural gas has a key role to play in transitioning our nation to a low-carbon economy."
Howarth acknowledged his statement contains many qualifiers but argued that there are sufficient concerns about the greenhouse gas emissions of hydraulically fractured natural gas to warrant early publication.
Critics also claim that fracking contaminates ground water with chemicals that are forced deep underground along with water and sand to fracture the shale and release its gas. (Editing by Marguerita Choy)
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